Infant swings, as well as the motor systems that control them, are well documented in the art. Traditionally, a swing consists of a seat which is supported at the distal end of one or more swing arms. A direct current (DC) motor is affixed between the support fame and swing arm such that the motor provides torque on one of the swing arms (the other being passively driven) to create the swinging motion of the seat. Existing art describes motor controllers that allow for a plurality of motion profiles which could be adjusted by means of a user interface. Previously, this was done by providing the motor with multiple, predetermined amounts of voltage, each producing a different torque from the motor and each corresponding to a motion profile. However, a swing operates on the principles of simple pendulum, and as such, the torque required from the motor to maintain a selected speed depends directly on the weight and location of the child in the seat. As a result, constant torque swings, although producing different motion profiles at each setting, also produce varying motion profiles for the same speed under different loading conditions, e.g., different sized children.
In an attempt to produce a consistent motion profile for each setting, under any loading condition, more recent art describes a feedback system which monitors the swing height at the end of each cycle and compares it to the desired swing height for the motion profile selected by the user. By comparing the desired swing arc with the actual swing arc, the motor controller can adjust the voltage to the motor and thus the torque it provides on the successive swings. This system, while providing a more consistent motion profile under various loading conditions for the same swing, still operates under the principles of pendulum, and as such, the speed of the seat increases as it moves away from the endpoints of the motion path. Because this system is limited to varying the motor torque once per cycle, the motor provides an inconsistent velocity profile over the motion path, resulting in peak and valley type velocity changes.